A head-mounted display device (HMD) which is a display device mounted on a head is known. The head-mounted display device allows a user to recognize a virtual image, for example, by generating image light indicating an image using a liquid crystal display and a light source and guiding the generated image light to the user's eyes using a projection optical system, a light guide plate, or the like.
PTL 1 describes a technique capable of displaying a virtual image at a distance on which a user's eyes are focused in such a head-mounted display device. In the technique described in PTL 1, a sensor senses sight lines of a user's right and left eyes and virtual image distance control means controls movement of display panels corresponding to the user's right and left eyes on the basis of the directions of the sensed sight lines. Accordingly, in the technique described in PTL 1, it is possible to change a focal distance of an image in a virtual image which is visually recognized by the user.